1. Field of the Invention
This invention relates to an apparatus for distributing sheet members and, more particularly, to a sheet distributor of the bin moving type, which distributes sheets by moving a group of bin trays relative to a sheet discharging means.
2. Description of the Prior Art
Conventional sheet distributors of this kind have a construction such as that shown in FIG. 1.
A sheet sorting unit 32 is connected to an image forming apparatus 31 which has a pair of transport rollers 36 for transporting a sheet member 5 on which an image has been formed and a pair of discharge rollers 6 for discharging the sheet member 5 out of the image forming apparatus.
The sheet sorting unit 32 has a pair of transport rollers 40 for transporting the sheet member 5 discharged from the image forming apparatus 31, discharge rollers 41, a guide plate 42 disposed between the transport rollers 40 and discharge rollers 41 to form a guide path 12, a bin unit 46 having a plurality of bin trays 45 (45a to 45j), and other components known to those skilled in the art. The bin unit 46 is moved in the direction of arrow 47 or 49 relative to the pair of discharge rollers 41 by an unillustrated lift mechanism so that a selected one of the group of bin trays 45 faces the pair of transport rollers 41. A sheet sensor 50 for detecting the sheet member in the guide path 12 is provided at a suitable position on the guide plate 42.
The operation of this sheet sorting unit will be described below with reference to corresponding step numbers of the timing chart of FIG. 3 of the accompanying drawings.
1: When image formation in image forming apparatus 31 is started, a start signal is sent from image forming apparatus 31 to sheet sorting unit 32.
2: In response to the start signal from image forming apparatus 31, transport rollers 40 and discharge rollers 41 rotate in the direction for transporting and discharging sheet member 5, and bin unit 46 is moved downward in the direction of arrow 49 to be set in a home position H.P such that the uppermost bin tray 45a faces the pair of discharge rollers 41 and bin unit 46 is ready for sheet discharge.
3: Sheet member 5 is discharged from the image forming apparatus 31, is fed into guide path 12 by transport rollers 40 and is detected in guide path 12 by sheet sensor 50.
4: Sheet member 5 is discharged into bin tray 45a by the pair of discharge rollers 41.
5: The trailing end of sheet member 5 passes the sensing position of sheet sensor 50.
6: When a predetermined length of time after the time point 5 has passed, the trailing end of sheet member 5 passes through the nip between the pair of discharge rollers 41, the bin unit lift mechanism (not shown) is driven.
7: By the operation of the bin unit lift mechanism, bin unit 46 is shifted upward in the direction of arrow 47, a distance corresponding to one bin tray, so that bin tray 45b faces the pair of discharge rollers 41.
8: The sorting unit is maintained in a waiting state to prepare for discharge of second sheet 5.
9: Thereafter, second sheet 5 is discharged from image forming apparatus 31, and the same operation as the step 3 is started.
Subsequently, the same operations as steps 4 to 9 are repeated, thus performing sorting and transportation of sheet members 5.
After a predetermined number of sheets have been distributed by moving the group of bin trays upward, other sheet members are distributed in the same manner while moving the group of bin trays downward.
The condition of sheet members distributed by moving the group of bin trays upward and the condition of sheet members distributed by moving the group of bin trays downward are as described below.
FIG. 2(a) is a diagram of a case of discharging the sheet member into one of the group of bin trays while moving the group of bin trays downward. A predetermined time after passage of the trailing end of the sheet member through the position of the sensor 50, downward movement of the group of bin trays is started. In this case, if, for example, bin tray 45b starts moving downward before the sheet member lands on the bin tray 45b, the locus of the trailing end of the sheet member to be landed on the bin tray 45b is formed as indicated by arrow A so that the sheet member glides through a long distance, as the bin tray 45b is shifted from the position indicated by the dot-dash line to the position indicated by the solid line. That is, the bin tray moves in the same direction as the glide-falling of the sheet member. This phenomenon is particularly noticeable when the sheet sorter is used in combination with a high-speed printer in such a manner that the sheet discharge interval is short. It is considered that in this discharge condition the gliding terminates when the trailing end of the sheet member going backward is brought into contact with a bent end portion 45.sub.1 formed as an end guide of the bin tray.
FIG. 2(b) is a diagram of a case of discharging the sheet member into one of the bin trays while moving the group of bin trays upward. In this case, if the upward movement of the group of bin trays is started before the sheet member lands on the bin tray, the locus of the trailing end of the sheet member to be landed on the bin tray 45b is formed as indicated by arrow B so that the gliding distance is shorter, as the bin tray is shifted from the position indicated by the dot-dash line to the position indicated by the solid line. This is because the bin tray is moved toward the sheet member. This phenomenon is also particularly noticeable when the sheet sorter is used in combination with a high-speed printer in such a manner that the sheet discharge interval is short.
As shown in FIGS. 2(a) and 2(b), the distance through which the sheet member glides (stays in the air) varies with respect to the upward and downward movements of the bin tray, so that sheet members discharged into the bin tray will not normally be uniformly placed and laid on each other, resulting in a sheet return failure or disorder of sheets.